Re: [PATCH v6 8/9] Implement kernel live patching for ppc64le (ABIv2)

[Denis Kirjanov]

On 1/25/16, Torsten Duwe <duwe@xxxxxx> wrote:
>   * create the appropriate files+functions
>     arch/powerpc/include/asm/livepatch.h
>         klp_check_compiler_support,
>         klp_arch_set_pc
>     arch/powerpc/kernel/livepatch.c with a stub for
>         klp_write_module_reloc
>     This is architecture-independent work in progress.
>   * introduce a fixup in arch/powerpc/kernel/entry_64.S
>     for local calls that are becoming global due to live patching.
>     And of course do the main KLP thing: return to a maybe different
>     address, possibly altered by the live patching ftrace op.
>
> Signed-off-by: Torsten Duwe <duwe@xxxxxxx>
> ---
>  arch/powerpc/include/asm/livepatch.h | 45 +++++++++++++++++++++++++++++++
>  arch/powerpc/kernel/entry_64.S       | 51
> +++++++++++++++++++++++++++++++++---
>  arch/powerpc/kernel/livepatch.c      | 38 +++++++++++++++++++++++++++
>  3 files changed, 130 insertions(+), 4 deletions(-)
>  create mode 100644 arch/powerpc/include/asm/livepatch.h
>  create mode 100644 arch/powerpc/kernel/livepatch.c
>
> diff --git a/arch/powerpc/include/asm/livepatch.h
> b/arch/powerpc/include/asm/livepatch.h
> new file mode 100644
> index 0000000..44e8a2d
> --- /dev/null
> +++ b/arch/powerpc/include/asm/livepatch.h
> @@ -0,0 +1,45 @@
> +/*
> + * livepatch.h - powerpc-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2015 SUSE
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#ifndef _ASM_POWERPC64_LIVEPATCH_H
> +#define _ASM_POWERPC64_LIVEPATCH_H
> +
> +#include <linux/module.h>
> +#include <linux/ftrace.h>
> +
> +#ifdef CONFIG_LIVEPATCH
> +static inline int klp_check_compiler_support(void)
> +{
> +#if !defined(_CALL_ELF) || _CALL_ELF != 2 ||
> !defined(CC_USING_MPROFILE_KERNEL)
> +	return 1;
> +#endif
> +	return 0;
> +}
This function can be boolean.
> +
> +extern int klp_write_module_reloc(struct module *mod, unsigned long type,
> +				   unsigned long loc, unsigned long value);
> +
> +static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +{
> +	regs->nip = ip;
> +}
> +#else
> +#error Live patching support is disabled; check CONFIG_LIVEPATCH
> +#endif
> +
> +#endif /* _ASM_POWERPC64_LIVEPATCH_H */
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 9e98aa1..f6e3ee7 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -1267,6 +1267,9 @@ _GLOBAL(ftrace_caller)
>  	mflr    r3
>  	std     r3, _NIP(r1)
>  	std	r3, 16(r1)
> +#ifdef CONFIG_LIVEPATCH
> +	mr	r14,r3		/* remember old NIP */
> +#endif
>  	subi    r3, r3, MCOUNT_INSN_SIZE
>  	mfmsr   r4
>  	std     r4, _MSR(r1)
> @@ -1283,7 +1286,10 @@ ftrace_call:
>  	nop
>
>  	ld	r3, _NIP(r1)
> -	mtlr	r3
> +	mtctr	r3		/* prepare to jump there */
> +#ifdef CONFIG_LIVEPATCH
> +	cmpd	r14,r3		/* has NIP been altered? */
> +#endif
>
>  	REST_8GPRS(0,r1)
>  	REST_8GPRS(8,r1)
> @@ -1296,6 +1302,27 @@ ftrace_call:
>  	mtlr	r12
>  	mr	r2,r0		/* restore callee's TOC */
>
> +#ifdef CONFIG_LIVEPATCH
> +	beq+	4f		/* likely(old_NIP == new_NIP) */
> +
> +	/* For a local call, restore this TOC after calling the patch function.
> +	 * For a global call, it does not matter what we restore here,
> +	 * since the global caller does its own restore right afterwards,
> +	 * anyway. Just insert a KLP_return_helper frame in any case,
> +	 * so a patch function can always count on the changed stack offsets.
> +	 */
> +	stdu	r1,-32(r1)	/* open new mini stack frame */
> +	std	r0,24(r1)	/* save TOC now, unconditionally. */
> +	bl	5f
> +5:	mflr	r12
> +	addi	r12,r12,(KLP_return_helper+4-.)@l
> +	std	r12,LRSAVE(r1)
> +	mtlr	r12
> +	mfctr	r12		/* allow for TOC calculation in newfunc */
> +	bctr
> +4:
> +#endif
> +
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  	stdu	r1, -112(r1)
>  .globl ftrace_graph_call
> @@ -1305,15 +1332,31 @@ _GLOBAL(ftrace_graph_stub)
>  	addi	r1, r1, 112
>  #endif
>
> -	mflr	r0		/* move this LR to CTR */
> -	mtctr	r0
> -
>  	ld	r0,LRSAVE(r1)	/* restore callee's lr at _mcount site */
>  	mtlr	r0
>  	bctr			/* jump after _mcount site */
>  #endif /* CC_USING_MPROFILE_KERNEL */
>  _GLOBAL(ftrace_stub)
>  	blr
> +
> +#ifdef CONFIG_LIVEPATCH
> +/* Helper function for local calls that are becoming global
> +   due to live patching.
> +   We can't simply patch the NOP after the original call,
> +   because, depending on the consistency model, some kernel
> +   threads may still have called the original, local function
> +   *without* saving their TOC in the respective stack frame slot,
> +   so the decision is made per-thread during function return by
> +   maybe inserting a KLP_return_helper frame or not.
> +*/
> +KLP_return_helper:
> +	ld	r2,24(r1)	/* restore TOC (saved by ftrace_caller) */
> +	addi r1, r1, 32		/* destroy mini stack frame */
> +	ld	r0,LRSAVE(r1)	/* get the real return address */
> +	mtlr	r0
> +	blr
> +#endif
> +
>  #else
>  _GLOBAL_TOC(_mcount)
>  	/* Taken from output of objdump from lib64/glibc */
> diff --git a/arch/powerpc/kernel/livepatch.c
> b/arch/powerpc/kernel/livepatch.c
> new file mode 100644
> index 0000000..564eafa
> --- /dev/null
> +++ b/arch/powerpc/kernel/livepatch.c
> @@ -0,0 +1,38 @@
> +/*
> + * livepatch.c - powerpc-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2015 SUSE
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#include <linux/module.h>
> +#include <asm/livepatch.h>
> +
> +/**
> + * klp_write_module_reloc() - write a relocation in a module
> + * @mod:       module in which the section to be modified is found
> + * @type:      ELF relocation type (see asm/elf.h)
> + * @loc:       address that the relocation should be written to
> + * @value:     relocation value (sym address + addend)
> + *
> + * This function writes a relocation to the specified location for
> + * a particular module.
> + */
> +int klp_write_module_reloc(struct module *mod, unsigned long type,
> +			    unsigned long loc, unsigned long value)
> +{
> +	/* This requires infrastructure changes; we need the loadinfos. */
> +	pr_err("lpc_write_module_reloc not yet supported\n");
> +	return -ENOSYS;
> +}
> --
> 1.8.5.6
>
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